A method and such a device are known from DE 10 2008 029 453 A1.
A conventional motor vehicle with an internal combustion engine becomes slower because of engine drag torque if a driver takes their foot off the accelerator pedal.
In motor vehicles with an internal combustion engine (ICE) and an automatic transmission there is what is referred to as a coasting operating mode in which the drivetrain is opened automatically, usually by opening a clutch when the driver takes their foot off the accelerator pedal. The internal combustion engine can also be entirely switched off in the coasting operating mode during idle or, for example, in the case of an automatic start/stop means. In the coasting operating mode, the engine drag torque is eliminated in order to save fuel.
Various driver interactions such as, for example, activation of the brake pedal, the accelerator pedal or the gear speed selector lever cause the drivetrain to close, i.e. causing the coasting operating mode to end and giving rise to non-coasting vehicle behaviour. With this general logic, the driver has control over the activation and/or deactivation of the coasting operating mode and the driver can choose between the coasting operating mode and rolling with engine drag torque.
The coasting operating mode makes it possible to save fuel because on an essentially level road because the motor vehicle can roll farther in a propulsionless fashion than a motor vehicle with a manual clutch under the influence of the engine drag torque. In particular the engine drag torque becomes even larger if in phases without a propulsion request. The supply of fuel is not maintained at the idling level but is instead completely switched off (in a state called overrun fuel cut-off). Furthermore, the coasting operating mode gives the driver a driving sensation.